Most hip fractures occur in the presence of low bone mass. We postulate that our exercise intervention will maintain or increase bone mass in older individuals. The potential benefit would be a decrease in the risk for hip fracture. We further postulate that participants will gain other benefits, such as a reduction in risk factors for ischemic heart disease. Hypothesis: Twenty-four months of specific loading exercises of the hip will increase femoral bone mass in adult men and women, ages 65-74 years. Specific Aims: 1) To assess the effectiveness of a 2-year exercise intervention regimen on proximal femur bone mass measured by dual energy x-ray absorptiometry; 2) To assess the relative effect of the exercise intervention on bone formation and resorption in older adults; 3) To compare the adaptation in bone mass to exercise intervention in older adult men and women; 4) To determine the level of compliance with the exercise regimen upon completion of the original study duration. Design and Methods: Men and women between the ages of 65 and 74 years will be recruited for a 24 month randomized, placebo-controlled clinical trial on the use of exercise to increase femoral bone mass. During the intervention period volunteers will maintain a high calcium diet with adequate vitamin D intake. The placebo-controlled exercise group will perform non-weight-bearing flexibility and abdominal strengthening exercises. The exercise trained group will perform an intervention protocol designed to provide an aerobic component with specific loading on the proximal femur. This consists of walking, stair-climbing, and an indoor step-up routine developed by us. Our exercise regimen is based on the following principles: practicality, involvement of movements used in activities of daily living, use of minimal equipment, easy adaptation to home use. Biochemical markers of bone metabolism will be measured to assess the relative impact of exercise training on bone formation and resorption. Prior to randomization, volunteers will complete a nine month run-in period. Bone density will be measured at -9,-4.5,0,6,12,18,24 months. Bone markers will be measured at -9,0,12,24 months. In summary, this exercise intervention is designed to improve bone mass at the proximal femur by stimulating bone formation.